WO 2012/138495 describes optical stacks comprising a first optical film comprising a plurality of structures comprising an optically active portion designed primarily to provide optical gain and optionally an optically in-active bonding portion disposed on a first surface bonded to a second optical film with a light-transmissive adhesive layer such that a portion of the structures penetrate the adhesive layer and a separation is provided between the adhesive layer and the first surface. The optical stacks exhibit a combination of high peel strength and high retained brightness, particularly after aging.
The adhesive layer preferably comprises an interpenetrating network of the reaction product of a polyacrylate component and a polymerizable monomer and the adhesive layer has an elastic modulus ranging from 100 to 2000 MPa at 25° C.